1. Field of the Invention
The present invention relates to a speedup device for reciprocating cylinders which make use of hydraulic or pneumatic pressure which are of wide application, and more particularly, it relates to a device for speeding up the extension of the rod of such reciprocating cylinder.
While there are many machines in which the speedup of the extension of the rod of a reciprocating cylinder is required, the invention is applied to the front loader of a transport and loading machine to speed up the extension of the rod of a cylinder, and hence the discharge rotation of the bucket of the front loader, thereby improving the efficiency of operation.
2. Description of the Prior Art
In the case of a machine in which a bucket pivoted to the front end of an arm is rotated to scoop earth, sand or other load and discharge it, a mere switching of a fixed amount of oil between the front and rear chambers of the cylinder results in different rates of extension and retraction of the piston rod.
This is due to the different volumes of the front and rear chambers of a reciprocating cylinder. More particularly, the volume of the front chamber where the piston rod exists is smaller than the volume of the rear chamber by an amount corresponding to the volume of the piston rod. As a result, when a case where a fixed amount of oil is fed into the rear chamber to extend the piston rod is compared with a case where the same amount of oil is fed into the rear chamber to retract the piston rod, it is seen that the rate of movement of the piston rod is higher in the latter case than in the former case. Therefore in the case of this machine, the rotative speed of the bucket is high when scooping earth, sand or other load but low when discharging it. With this, the efficiency of operation cannot be improved.
In machines, including those using hydraulic cylinders, much time and money has been involved in improving the efficiency of operation. This is because the measures taken have been to increase the size and capacity of hydraulic pumps and electric motors so as to increase the rate of extension of the reciprocating cylinder rod. Accordingly, there has been a disadvantage that these measures make it necessary to increase the size of the pipe line and additionally install a link system, thereby further increasing the cost.
As a recent measure to eliminate these drawbacks, there has been known what is called a boost valve (refer to the June, 1976 issue of the magazine "Yuatsuka Sekkei" (Hydraulic Design).) It includes three check valves which are arranged in parallel so that oil may flow in predetermined directions and part of the return oil from the front chamber of the cylinder may join oil from a pump in front of a control valve, thereby increasing the rate of extension of the cylinder rod. Therefore, this arrangement makes it necessary to increase the size of control valves and pipes.